1. Field of the Invention
The present invention relates to a log file control system used in a complex system for controlling log data of a data base shared among a plurality of computer systems, and more specifically to a log file control system for use in a complex system for controlling a log file such that each computer system performs a high-speed transaction.
2. Description of the Related Art
A complex system refers to a system consisting of a plurality of computer systems connected to one another via communication lines. Each of the computer systems forming the complex system may be hereinafter referred to as a cluster. Diversified and large-scale computer systems have enabled such complex systems to be widely utilized in many fields in industry.
When resources are shared in a complex system, one cluster is kept waiting if another cluster is using the shared resources. The wait for a transaction causes a delay in data processing. Accordingly, a complex system should be designed such that a wait for a transaction can be as short as possible.
Conventionally, when a data base is shared in a complex system, an accumulation file (log file) containing log data, that is, updated data of the data base, is provided for each cluster.
Lately, when a data base is shared in a complex system it can be accessed by only one cluster through a reserve release which is a hardware mechanism. When a log file is shared in a complex system, the file is expected to be accessed by only one cluster, as in the above described method of sharing a data base, through a reserve release by a hardware mechanism. However, in such a configuration, an exclusive lock control is performed in units of volume and the transactions of clusters to which access cannot be made are kept waiting, resulting in poor efficiency in processing transactions in the entire system.
Then, when a data base is shared conventionally in a complex system, a log file is provided for each cluster so that delays will not be caused by a waiting state due to the exclusive control.
According to Japanese Patent Application No. Tokugan-Hei 3-289031 (titled "Inter-system Exclusive Control Method"), the above-recited invention has disclosed that shared resources are not controlled in a large-volume unit, but in a smaller exclusive unit according to an exclusion table, provided in a semiconductor storage unit in a complex system, for controlling shared resources. The invention does not utilize the conventional reserve release by a hardware mechanism.
According to the above-recited invention, a data base can be controlled in a block-exclusive unit when the data base is shared in a complex system. That is, when a block of the data base is being updated during a transaction in the computer system, all the other transactions in the complex system cannot update the block until the current transaction has finished its process. Actually, if a transaction tries to update a block being updated by another transaction, it is kept waiting until the updating transaction has finished with the block.
Thus, even with the conventional configuration containing a log file for each cluster, the above-recited invention reduces the exclusive or locking unit of a shared data base, the exclusive or locking operation being reduced more than in an exclusive or locking operation performed in units of a volume. This results in a great improvement towards complete solving the problem of waiting for transactions.
However, if a log file is provided for each cluster as in a conventional method, then the invention requires the rearrangements of log data generated by clusters in sequence of their generation among the clusters, thereby requiring quite a complicated recovery process. Therefore, the performance is reduced considerably in processing transactions. Thus, complete transactions cannot be processed at a high speed.